1. Field of the Invention
Apparatus and process for practice therein for reduction of sodium hydroxide with natural gas in the presence of heat to produce sodium metal as a product of the thermodynamic reaction.
2. Prior Art
The invention is in a reactor vessel wherein sodium hydroxide is introduced in liquid form and reacted with natural gas or methane gas at temperatures between one thousand and eleven hundred degrees C., in a bath of sodium carbonate, with the reactants vaporized and then separated or reduced by a rapid cooling with their passage onto a cooled surface located within a quench cooler or by an introduction of a coolant liquid flow, such as mineral oil, into the gaseous reactants, to condense liquid sodium out of a vapor phase. Liquid sodium as is produced is then drained from the reactor vessel, in a continuous process. The reactor vessel and quench cooler are maintained with an inert atmosphere and the quench cooler is maintained at a pressure that is less than atmospheric, minimizing an unwanted reverse or back reaction of sodium from its metal state due to a scarcity of unreacted molecules such as are present when sodium metal is liquified in prior art quench systems.
Apparatus and processes for refining sodium metal are old in the art. Some examples of earlier apparatus and processes are shown in U. S. Pat. No 342,897 to Castner; U.S. Pat. Nos. 380,775 and 380,776 to Thowless; and U.S. Pat. No. 460,985 to Netto, that generally have involved a carbonaceous material as a reactive agent, that is usually carbon or coke in powder form, and is intended to react with a compound containing sodium or potassium, in the presence of high heat, to produce free sodium. Such processes not only require that a number of complex steps be performed to finally produce sodium metal and further they are generally single batch processes only. Whereas, the system and process of the invention provide for a continuous refinement of sodium metal from a mix of sodium hydroxide as a reactant and, preferably, natural gas as a reductant, with the invention utilizing a flow through system where the reactants are heated by a molten sodium carbon bath with, on further exposure to heat they are then vaporized. That vapor is then rapidly cooled or quenched in a quench cooler, condensing sodium metal that can then be drawn off, with the process steps taking place as a continuous process.
In a French Patent No. 603,825, sodium metal is set out as produced utilizing sodium hydroxide and iron in power form by first vaporizing the mix with the temperature of the mix then lowered to below the sodium vaporization temperature, condensing sodium metal therefrom. This process, however, must be conducted in a vacuum and requires removal of the sodium from a reaction zone to condense it. Further, the French '825 patent is like a U. S. Pat. No. 2,642,347 to Gilbert, that provides for a production of sodium metal vapor from a condensation of sodium carbonate that has been reacted with carbon at high heat of from 1000 degrees C. to 1200 degrees C., with the sodium metal vapor then conducted away from the reaction. The condensation step set out in the Gilbert '347 patent utilizes surfaces of steel balls that are individually maintained at a temperature below that required for sodium vaporization so as to condense sodium metal out of the vaporized reactants as a film on the individual ball surfaces that then must be removed, providing a batch process only. The above cited systems are each essentially batch systems only unlike the present invention that is a continuous system with sodium metal produced in liquid form that is then drawn from a quench cooler of the reaction system. Further, unlike the invention, none of the above cited patents, no the patents cited below have involved a use of sodium hydroxide and methane as reactants for a continuous system. Nor have either of the systems of these French '825 and U.S. '347 patents proved a novel reactor vessel and quench cooler configuration like that of the invention where the sodium compound is vaporized and then condensed as sodium metal at either a condensation plate that is maintained at a temperature below the temperature where a vaporized sodium metal will liquify, or by a counter current flow of a non-reactive liquid, such as mineral oil, providing for quenching sodium metal from the gaseous product from the reactor vessel, with the condensed sodium metal then drained from system into a separate vessel.
A U. S. Pat. No. 2,930,689 to McGriff teaches a submerged combustion of methane in molten sodium carbonate solution and includes a separation wall to prevent the combustion gasses, water and carbon dioxide, from entering into the reaction of methane or carbon with sodium carbonate. The McGriff process requires a high operating temperature of from 1150 to 1250 degrees C., with carbon or methane fed into the hot sodium carbonate, and with sodium carbonate continuously added. The sodium carbonate, like the invention, providing a heat sink but, unlike the invention, also provides for a reduction of the sodium carbonate with a continuous addition of carbon, preferably coke in powdered form, to perpetuate the reaction. The McGriff '689 utilizes a rectangular reactor vessel that employs a baffle as a separator and is precluded by its constriction from effectively utilizing an electrical heating strategy may be incorporated in the invention.
While McGriff '689, like the invention, teaches a use of methane as one of the reactants for producing sodium metal, the other reactant of McGriff, unlike the invention, is preferably a molten sodium carbonate and further requires that carbon, in powdered form, be continuously passed into the reaction vessel. Further, unlike the invention, the McGriff '689 provides for burning of methane forming, as a product of combustion, water and carbon dioxide, with the water and carbon dioxide then prohibited from entering into a reaction of methane or carbon and with sodium carbonate reduced to produce sodium metal. The process of the McGriff '689 patent requires high heat with methane fed into very hot sodium carbonate and further requires that sodium carbonate be continuously added. This system not only requires a greater heat than which is required in the invention to produce the required reactions, it also requires an addition of solid coke in powdered form to provide the carbon required for the reaction to proceed. Unlike the system and process of the McGriff '689 patent, the present invention utilizes methane reductant with sodium hydroxide, that can be and preferably is an industry waste, does not reduce sodium carbon that serves only to provide heat as would require that carbon be added to perpetuate the reaction, is practiced as a continuous process and with the system shut down, provides an ease of access into the reactor vessel for performing maintenance tasks. Further the McGriff '689 patent does not deal with problems as are inherent in quenching vaporized sodium from a mix of gaseous carbon monoxide (CO) and sodium (Na), in that it fails to recognize and deal with a back reaction as will occur as the gases cool, with sodium tending to react with carbon monoxide, to produce sodium carbonate (Na2CO3), which problem the present invention addresses and solves.
A U.S. Patent to Deyrup, et al. U.S. Pat. No. 2,685,346, includes a step of quenching a hot vapor containing a free alkaline metal so as to condense that alkaline metal into a molten state, and deals peripherically with handling of a back reaction as the alkaline metal vapor is quenched, where carbon monoxide combines with the gaseous alkaline metal. Restricting such unwanted back reaction in Deyrup '346 is, however, very tedious and, unlike the system and steps of the invention, it involves an infusion of large amounts of tin and requires that the process take place, at a high temperature, and involves elaborate valves to handle such high temperature. Further, a to Deyrup et al., U.S. Pat. No. 2,685,346 teaches a multi-step process to provide for a quenching of the sodium metal from a vaporous mixture with carbon monoxide and hydrogen and is tedious in that, in its practice, it is likely that sodium will become entrained with nitrogen gas, thereby markedly reducing the sodium metal yield. Further, the system of the Deyrup, et al. '346 patent is not continuous.
Like the McGriff patent, an earlier to Bowe, U.S. Pat. No. 2,484,266, also involves a quenching step but does not, as does the present invention, handle to limit a resulting back reaction. Further the Bowe '266 patent utilizes iron in the form of ferro phosphorus into which alkali carbonates or hydroxides are introduced and is apparently practiced as a batch process only with that practice taking place in a vessel that is structurally very different from the reactor vessel and quench cooler of the present invention.
Other earlier processes and devices for producing sodium metal, and the like, utilizing metal vapor separation, include additional to the above cited to Deyrup, et al., U.S. Pat. No. 2,685,346, a later Deyrup, et al. U.S. Pat. No. 2,685, 505, that each set out a reactor vessel and process for practice therein that involves a distillation of a sodium or other alkali metal formed from a reduction of carbon with sodium compounds and with a separation of sodium from the mixture of sodium vapor and carbon monoxide resulting from a sodium carbonate reduction undertaken in the presence of molten tin. In both those patents, unlike the invention, the molten tin absorbs sodium metal out from the gas mixture with carbon monoxide passed unchanged therefrom, whereafter, the molten tin has absorbed sufficient sodium to form a sodium tin alloy that contains from one to seven percent by weight of sodium, the system must be shut down and the sodium tin alloy removed. Thereafter, the sodium metal is recovered from the molten tin alloy by exposing it to an inert gas, such as nitrogen, that removes the bulk of the sodium from the sodium alloy above the boiling point of sodium and with the resulting mixture of inert gas and sodium vapor then cooled to condense out liquid sodium metal that is in a substantially pure state. Both the Deyrup, et al. processes involve elaborate high temperature values and a multi-step quenching process to quench metallic sodium from the gaseous mix and, in practice, a large percentage of sodium will be entrained in the nitrogen gas. Unique therefrom, the reactor vessel and quench cooler and process for practice of the invention provide for condensation of liquid sodium metal directly out from a mix of gaseous carbon monoxide and hydrogen at less than atmospheric pressure, which less than atmospheric pressure reduces the presence of molecules as could contribute an unwanted back reaction. The process of the invention, unlike earlier processes, is simple and efficient and does not require a binding of the sodium with tin or any other metal. Further, carbon monoxide and hydrogen gas as is separated out from the gaseous mix when sodium is quenched is then useful for burning, along with added fuel, to produce heat in the reactor vessel that produces a heating of a sodium carbonate bath that transfers heat to the sodium hydroxide as it is drawn combined with a methane reductant. After quenching, the condensed sodium metal is available to be draw from the reactor system quench cooler, providing for a continuous sodium production.